如何在JPanel中移动图形的位置

Question

So I'm creating a game using Javax.swing library for my uni coursework. I have created a window and I have successfully written code to procedurally generate a game map.

However, I am unable to change the focus of the map. What I mean is that the map is always stuck in one corner of the screen. (IE: Location is set to 0,0, hence the Graphics g (the map) is put in that location going outwards.)

I would like to be able to move the "camera" so that different areas of the map can be viewed by the player.

Bellow I have pasted my method that draws the map onto the screen. Could anyone tell me what I could do to have the camera move at runtime. AKA: to shift the map left or right.

I thought of having a Graphics object that will hold the map, and then I'd only draw a subImage of that Graphics object, but considering how the map will be redrawn every frame (For animation purposes) that just means that I'll have even more graphics to redraw. The map is 6,400 * 6,400 Pixels

@Override
protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    try {
        for(int x = 0; x < OverworldMap.MAP_X_SIZE; x++){
            for(int y = 0; y < OverworldMap.MAP_Y_SIZE; y++){
                for(int layer = 0; layer < OverworldMap.MAP_LAYER_SIZE; layer++) {
                    g.drawImage(OverworldMap.getTileAt(x, y, layer).getSprite(), x * SPRITE_SIZE, y * SPRITE_SIZE, null);

                }
            }
        }
    } catch (Exception e) {
        LauncherClass.printErrorLog(e);
    }
}

Answer 1

The best / easiest way to solve this is to put a JScrollPane around your JPanel, and make the JPanel the size of your image. You don't need to worry about only repainting the right part of your image - Java is pretty smart about only drawing the parts that are on screen. Note that you can show or hide the ScrollBars, but if you hide them you need to add logic to activate scrolling through some other mechanism

Answer 2

You cannot store a Graphics object and use it later. It is only valid for the duration of the paint method to which it is passed.

You can, however, simply offset your painting:

Image sprite = OverworldMap.getTileAt(x, y, layer).getSprite();
g.drawImage(sprite, x * SPRITE_SIZE - playerX, y * SPRITE_SIZE - playerY, this);

(Notice that the last argument to drawImage should be this .)